I\'m getting strange occurance on our servers when I am trying to send an email using SmtpClient class via an ASP MVC3 project. This is the code I am using.
It is likely that the mail server does not support sending anonymous emails and will require credentials to be specified which are registered on the mail server.
You can specify the credentials like so:
client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("username", "password");
Hope this helps.